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johnmil 15th December 2010 03:56 PM

Eico HF-89a question
 
Eico HF-89A question. Does someone have a schematic of the Eico HF-89a? My specific need is to know the value and location the low value capacitor that is attatched to the grid of V 2 and V 3. What is the location of the other end of this capacitor and the value?

SY 15th December 2010 04:06 PM

0.25 microfarad/400V. You can use 0.33u, which will probably be easier to source. It goes between grid and ground.

no gas 15th December 2010 04:19 PM

Quote:

Originally Posted by SY (Post 2399498)
0.25 microfarad/400V. You can use 0.33u, which will probably be easier to source. It goes between grid and ground.

Solen makes a .27uF 630VDC for less than $2 each, one of the few actual .27uF caps out there and good for Mcintosh rebuilds too.

SY 15th December 2010 04:51 PM

There ya go!

johnmil 15th December 2010 05:43 PM

I should have been more clear. Sorry
 
Tubes V 2 and V3 are a dual tube - 6SN7. I am asking about the grid for the first tube - pin #1.

SY 15th December 2010 05:47 PM

Right. Pin 1 is bypassed to ground via that 0.25uF cap. Pin 1 is also connected to pin 4 via a 1M resistor.

V2 is Channel 1, V3 is channel 2. The other sections of those tubes (grid pin 4) are direct coupled to the input tube plate.

johnmil 15th December 2010 06:08 PM

Yes, but ----
 
Sorry, I am not asking about the 0.25 mf capacitor.
The capacitor I am asking about is a change brought
about when EICO changed vendors of the output
transformer. The HF-87 and first version of the HF-89
had a 750uuf placed across one half of the transformer
primary to deal with phase shift in the transformer. This
capacitor was replaced in the HF-89a. According to
old posts in the EICO Yahoo group. The new "fix" was
a "low value capacitor at the input of the 6SN7. The
amp I recently purchased does not have this capacitor
but I think I can see where it was cut off of pins 1
of each 6SN7. If someone has a 89A schematic, I
need to know the value and location of this capacitor.
Again, I am not asking about the 0.25 mf capacitor you
describe. I feel the cap. would somehow be connected
to pin four or five of V4 and V5. Thanks for your help.


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